No one seems to try to protect the buyers of that labor. 

What’s the best course for me to take to try to protect myself?

I am just starting to read about it and finding the idea of "self-directing"  very inspiring and at the same time scary -- much like how I feel about real estate investment, in general :) Does anyone have a recommendation for a good CPA with expertise both in self directed IRA and REI in or near Westchester, NY?

That means you would follow the same steps as above to establish the same protection of a LLC for Sibling #1 and yourself - then writing an Operating Agreement that would once again state how you two would want to operate this property now and into the future.

In addition, your costs normally over run on these smaller projects because the GC who handles the funds will need to protect themselves by building in a significant cost buffer. 

In theory you are better protected with the LLC, I'm speculating but if you screw up really bad and somebody dies on your property due to your negligence the LLC or individual ownership is not going to matter, you're going to be in a world of hurt either way.

I've read plenty of articles on here about protection from cash buyers going behind my back but no one is really saying anything useful.

Thanks @Kurt Michaelson, I've seen many of these "wholesale" contracts, unfortunately I don't think they are detailed enough to protect me.

DefaultSouth Carolina offers fewer formal protections to buyers under land contracts than the laws of many other states.

Also, in the future have all your tenants sign a mold addendum which definitely protects you prior to such issues.I would force them out by giving them a proper notice from your LEASE terms, for example I can get my property back with a 60 day notice period- which is the proper notice time by law here in Georgia.